In a gas turbine a compressor produces compressed air which is directed into a combustor. In the combustor the compressed air is mixed with fuel and burnt. The hot and pressurized gas exiting from the combustor passes through a turbine to drive a respective rotor.
In operation air is drawn into the staged compressor. Each stage of the compressor comprises a row of stator blades and rotor blades. The first rows of stator blades can be implemented as variable stator blades which are adjusted by actuation levers. The stator blades deflect the incoming air and direct it onto the airfoils of the rotor blades for compression. The variation of the stator blades allows for load changes of the gas turbine.
In such compressors, measures have to be taken to prevent compressor blade spindle seizure. For example, seized out of position stator blades can cause turbulent effect on adjacent downstream stages of rotor blades, possibly accelerating cyclic fatigue of the rotor blades. Another issue that is to be addressed is that overloading and subsequent bending of one or many variable compressor blade actuation levers can occur. Individual variable compressor blade stage push rods can be overloaded and subsequently bended. Finally, the engine can trip to idle speed due two out of position blades. Also, a combination of these issues can take place.
In FIGS. 1 and 2 prior art assemblies of variable stator blades are shown. FIG. 1 shows a variable stator blade 2 with a spindle 4 and sections 5, 7, 9 and 11.
The spindle 4 is placed inside a bearing bush 10 which is placed in turn within a spindle bush 8. The spindle bush 8 is surrounded by a casing 6 with a counterbore 18. The section 9 holds a seal 12 with adjacent o-rings 14 on sections 7 and 11. Between the spindle bush 8 and the o-ring 14 on section 7 there is a thrust washer 16.
Wear to the seal edge 13 of the seal 12 can cause reduction of sealing between the casing 6 and the variable stator blade 2.
In FIG. 2, another arrangement of a variable stator blade assembly is shown. The arrangement is substantially the same as in FIG. 1. Here, no seal 12 is present. Instead, the sealing is achieved by an o-ring 14 placed between the section 7 of the compressor blade 2 and the thrust washer 16.
In this arrangement moisture can enter the counterbore 18 from the gap 17 between counterbore wall of the casing 6 and the compressor blade 2 if the sealing fails.
To provide a seal between a rotating part and a stationary part, several types of seals are known. Some of theses seals are disclosed in U.S. Pat. No. 6,161,834, JP 11248003, CA 2371537, JP 2002267021 and RD 393053.